This invention relates to magnetic amplifiers and more particularly to a particular construction for the gate winding of a magnetic amplifier.
Magnetic amplifiers have found use in electrical systems requiring relatively large power gains and isolation between the control circuitry and the output or load circuitry. For example, in high power distribution systems large magnetic amplifiers are commonly used for varying or regulating the magnitude of large amounts of power.
The term "magnetic amplifier" has been broadly applied to any static device employing saturable core reactors to provide amplification or control. The saturable core reactors employed in magnetic amplifier circuits generally have a core formed of magnetic material having a substantially rectangular dynamic hysteresis curve, i.e., the plot of flux density (B) against magnetizing force (H). When such core materials are used, the core of the reactor can be made to change from saturation in one direction to saturation in the opposite direction in response to a small change in magnetizing force. Saturable core reactors have a further characteristic of displaying very high impedance when their cores are unsaturated and very low impedance when saturated.
A magnetic amplifier in the broadest sense includes a saturable core reactor with its high current winding, referred to as a "gate" winding, connected in series with a load and a source of alternating current. It will thus be readily understood that when the reactor core is unsaturated, so that the reactor displays high impedance, minimum current will flow in the gate winding (and consequently in the load); conversely, when the reactor core is saturated with the reactor displaying low impedance, maximum current will flow in the gate winding. By causing the reactor core to go into saturation at some point during a half-cycle of applied AC voltage, it will be seen that the load current will be small during the first part of the half-cycle and large during the remainder. By varying the point at which the core goes into saturation, referred to as the firing angle, the duration of the impulses of highvalue load current and thus the average value of load current can be varied.
The core of the reactor is conventionally provided with a DC bias or control winding commonly energized from a source of adjustable DC voltage. The bias winding therefore provides a predetermined magnetomotive force (MMF) level in the core. The firing angle of a given core may be varied by providing it with a predetermined MMF (via the bias winding) so that after each half-cycle of applied AC voltage, the core returns to a predetermined point on its dynamic hysteresis curve of B-H characteristics. With the core beginning each half-cycle at a predetermined point on its B-H curve, as established by the bias winding current, the remaining MMF required to drive the core into saturation is provided by the current flowing in the gate winding. Since a small change in the bias voltage will provide a large change in the firing angle and thus the average load current, it is seen that a small control signal can be made to control a large load current.
As the load current, and thus the gate winding currents, increase in magnitude, the magnetic amplifiers become larger and the gate windings in particular become bulky and complicate the construction.